I can tell you right now what causes this in my case. I strongly believe I've pinpointed my trouble falling out of bed twice over a period of as many weeks. Although I'm 63 years old these are the only two times I have [ever] fallen out of bed in my whole life; and uninjured only skinning my arm on the night stand and a little knock on the head (no egg), my wife and I both laughed about it since this last episode woke her too. But unable to get back to sleep after being suddenly jolted awake, mildly dizzy and sublimely curious (maybe even a little suspicious) I decided to wobble into my workstation room and 'Google' this issue to see what was up. ...Great things computers!
On both occasions rolling off the bed while asleep I treated myself to two large goblets of red wine with dinner (Paisano). And, being relatively abstemious I never drink very much because of the following:
I'm taking a host of oral medications such as blood pressure pills; Type II diabetes meds (Glipizide and Metaformin); Simavastin for cholestorol; Atenolol; Lasix; Spironolactone; a 300mg. daily dose of cardiac prophylaxis aspirin, plus I'm an insulin-dependant diabetic. ...If this wouldn't cause somebody to fall out of bed, nothing would!